大质量年轻星体新的C18O(1-0)发射

利用紫金山天文台青海观测站13.7米的毫米波望远镜对74个大质量年轻星体或候选进行了C^18O(1-0)的谱线观测。在63个源中观测到了C^18O(1-0)发射，其中57个天体第一次探测到C^18O(1-0)谱线发射。根据谱线辐射温度（TR^*)和半宽（△V），利用LTE方法计算了每个测量源的C^18O(1-0)发射的光学厚度和C^18O(1-0)分子的柱密度。讨论了^13CO(1-0)和C^18O(1-0)的谱线强度比和积分强度比。     

具有硅酸盐尘埃特征碳星的新的候选者

本文根据红外天文卫星的宽波段测光及低分辨率光谱资料，给出了两颗新的可能具有硅酸尘埃特征的碳星及４颗可能的候选者。     

A High-accuracy, Small Field of View Star Guider with Application to SNAP

To accomplish its mission, the spaceborne observatory SNAP (SuperNova Acceleration Probe) requires a pointing stability of <0.03 arcseconds during exposures lasting up to 500 sec. A Monte Carlo simulation of the photoelectron statistics from the guiding star investigates geometrical (such as the pixel size of the detector or the plate scale) and physical parameters (such as the magnitude of the star). It is shown that simple centroiding calculations can lead to the desired accuracy with guide stars as faint as magnitude 16. Availability of these stars is verified thanks to the HST Guide Star Catalog complemented with a statistical model of the distribution of stars. Thus a through-the-lens sensor that uses stars as faint as magnitude 16 to provide the necessary guiding signals is feasible. This revised version was published online in July 2006 with corrections to the Cover Date.     

Narrow-band CCD photometry of giant H ii regions

We have obtained accurate CCD narrow-band Hβ and Hα photometry of giant H  ii regions (GEHRs) in M33, NGC 6822 and M101. Comparison with previous determinations of emission-line fluxes shows large discrepancies; their probable origins are discussed. Combining our new photometric data with global velocity dispersion ( σ ) derived from emission linewidths, we review the     relation. A re-analysis of the properties of the GEHRs included in our sample shows that age spread and the superposition of components in multiple regions introduce a considerable spread in the regression. Combining the information available in the literature regarding ages of the associated clusters, evolutionary footprints on the interstellar medium, and kinematical properties of the knots that build up the multiple GEHRs, we find that a subsample – which we refer to as young and single GEHRs – do follow a tight relation in the     plane.     

Comparisons of Infrared Colors and Emission-line Intensities between Two types of Seyfert 2 Galaxies

We study the relation between the infrared colors[ OⅢ] emission lines,gaseous absorbing column density(NH) ,and the detectability of the polarized (hidden)broad-line region(HBLR) in a large sample of 75 Seyfert 2 galaxies(Sy2s).From the indicators of star-formation activity,f60/f100 and LFIR/LB,we find some evidence that the Sy2s without HBLR show higher star-formation activities than those with HBLR,in agreement with previous prediction.Also,we confirm that the HBLR Sy2s tend to have a larger luminosity ratio of the core to the host galaxy,suggesting that the HBLR Sy2s display more powerful AGN activity.Howerver,the level of obscuration found in previous papers in nearly indistinguishable between the two types of Sy2s.The results support the statement that the non-HBLR Sy2s,with a weaker core component and a stronger star-formation activity component,are intrinsically different from the HBLR Sy2s,which are Sy1 systems with a hidden powerful AGN core and a low star-formation activity.The indications are that the non-HBLR Sy2s might be at an earlier evolutionary phase than the HBLR Sy2s.     

Hubble Space Telescope photometry of globular clusters in the Sombrero galaxy

We explore the rich globular cluster (GC) system of the nearby Sa galaxy M104, the 'Sombrero' (NGC 4594), using archive Wide Field Planetary Camera 2 data. The GC colour distribution is found to be bimodal at the >99 per cent confidence level, with peaks at     and     . The inferred metallicities are very similar to those of GCs in our Galaxy and M31. However, the Sombrero reveals a much enhanced number of red (metal-rich) GCs compared to other well-studied spirals. Because the Sombrero is dominated by a huge bulge and only has a modest disc, we associate the two subpopulations with the halo and bulge components, respectively. Thus our analysis supports the view that the metal-rich GCs in spirals are associated with the bulge rather than with the disc. The Sombrero GCs have typical effective (half-light) radii of ∼2 pc with the red ones being ∼30 per cent smaller than the blue ones. We identify many similarities between the GC system of the Sombrero and those of both late-type spirals and early-type galaxies. Thus both the GC system and the Hubble type of the Sombrero galaxy appear to be intermediate in their nature.     

Stellar contents of two young open clusters: NGC 663 and 654

UBVRI CCD photometry in a wide field around two young open clusters, NGC 663 and 654, has been carried out. Hα and polarimetric observations for the cluster NGC 654 have also been obtained. We use the photometric data to construct colour–colour and colour–magnitude diagrams, from which we can investigate the reddening, age, mass and evolutionary states of the stellar contents of the these clusters. The reddening across the cluster regions is found to be variable. There is evidence for anomalous reddening law in both clusters; however, more infrared and polarimetric data are needed to conclude about the reddening law. Both clusters are situated at about a distance of 2.4 kpc. Star formation in both clusters is found to be a continuous process. In the case of NGC 663, star formation seems to have taken place sequentially, in the sense that formation of low-mass stars precedes the formation of most massive stars. Whereas, in the case of NGC 654, formation of low-mass stars did not cease after the formation of most massive stars in the cluster.     

Nearby Protoclusters as Laboratories for Understanding Star Formation on Galactic Scales

Detailed studies of nearby cluster-forming molecular clouds can help us understand the physical processes by which most stars form in galaxies. I review recent advances made on this subject. Submillimeter observations of nearby protoclusters suggest that stars are generally built from finite, detached reservoirs of mass inside molecular cloud cores, and point to a cloud fragmentation origin for the IMF. Much progress in this field will come from future large submillimeter instruments such as Herschel and ALMA. This revised version was published online in September 2006 with corrections to the Cover Date.